Implantable medical device with integrated acoustic transducer

ABSTRACT

An implantable medical device comprises a hermetically sealed housing having a housing wall with an interior surface, and an ultrasonic acoustic transducer, the transducer comprising one or more piezoelectric discs fixed to the interior surface of the housing wall, such that the housing wall acts as a diaphragm in response to induced movement by the one or more piezoelectric material discs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/287,557, filed on Nov. 23, 2005, which claims priority under 35U.S.C. §119 to U.S. Provisional Patent Application Ser. No. 60/630,801,entitled “Implantable Medical Device With Integrated AcousticTransducer,” filed on Nov. 24, 2004, each of which are expresslyincorporated herein by reference in their entirety for all purposes.

FIELD OF INVENTION

The present invention relates to the field of diagnostic and therapeuticmedical implants and data communication between them.

BACKGROUND

Communication between diagnostic and/or therapeutic medical deviceimplants within the body can be highly beneficial. One example is theinformation exchange between an implantable sensor and an implantablepulse generator (IPG), that uses the sensed information for optimizingits operation. Published U.S. Patent Application US 2004-0204744A1,which is incorporated by reference herein, discloses using an intra-bodyacoustic communication link for this purpose. As taught in thatpublication, in order to minimize energy consumption, the sensor implantis left deactivated (i.e., not powered on) until an acoustic wave pulsereceived from another implanted device activates the sensor implantusing acoustic switch technology. Two possible transducer configurationsapplicable for this concept are disclosed in this published application.

Acoustic transducers integrated in implantable medical devices areknown. For example, U.S. Pat. No. 6,477,406, discloses several acoustictransducer configurations used for listening to sounds produced by theheart. However, these transducers were designed only for receivingacoustic signals, and not for transmitting acoustic signals. Moreover,the transducer configurations of this patent are optimized to low soundfrequencies in a range of 5-300 Hz, while for acoustic communicationmuch higher frequencies are used, e.g., in an ultrasonic range of 20kHz-10 MHz. In particular, U.S. Pat. No. 6,477,406 does not teach anacoustic transducer that can effectively produce ultrasonic transmissionor serve as an effective receiver at high acoustic frequencies.

Acoustic communication was also suggested for data exchange between animplantable device and external unit, such as disclosed in U.S. Pat. No.5,113,859. However, this patent also does not teach or describe anacoustic transducer capable of performing the communication, nor isthere any transducer disclosed or described that is capable oftransmitting ultrasonic signals at a level sufficient for activating anacoustic switch and/or communicating with a second implant.

SUMMARY

In one embodiment, an implantable medical device comprises ahermetically sealed housing having a housing wall with an interiorsurface. An ultrasonic acoustic transducer comprising one or morepiezoelectric discs is fixed to the interior surface of the housingwall, such that the housing wall acts as a diaphragm in response toinduced movement by the one or more piezoelectric material discs. Theone or more piezoelectric discs may comprise, for example, a materialselected from the group of materials comprising piezoelectric crystal,electro-active ceramics, ceramic-polymer composite, PVDF, and PVDFcopolymer. The transducer is preferably configured to operate at aresonance frequency that is between 20-200 KHz.

In embodiments of the invention, the device further comprises an annularring attached to the interior wall of the surface of the housing walland surrounding the one or more discs. The device may also furtherinclude a membrane interposed between the interior wall surface and thepiezoelectric discs, wherein the membrane has a substantially greaterthickness than the enclosure wall. For example, in one embodiment, themembrane is mounted on a pedestal, the pedestal attached to the wallsurface and having a smaller diameter than the piezoelectric discs.

In some embodiments, the interior wall may comprise an indent portiondefining a recess, wherein the transducer is mounted to the wall withinthe recess. In some embodiments, the one or more piezoelectric discscomprise two discs, and further comprising an electrode positionedbetween the piezoelectric discs, wherein a respective electrical lead iscoupled to each of the two discs and the electrode. An amplifier isintegrated with the one or more piezoelectric discs in order to minimizeparasitic effects and noises.

In some embodiments, the one or more transducer discs may comprise asingle disc attached about an outer circumference of the disc to asupport structure, the support structure attached to the enclosure wallsurface and elevating the transducer disc from the wall so as to allowthe disc to flex into a space defined between the disc and the enclosurewall. The support structure may comprise, for example, a membraneinterposed between the interior wall surface and the piezoelectric disc.In such embodiments, the membrane may be mounted on a pedestal, thepedestal attached to the wall surface, wherein the pedestal has asmaller diameter than does the piezoelectric disc. In embodiments of theinvention, the transducer may be a flexural type or a flex-tension typeacoustic transducer.

In accordance with a further embodiment of the invention, an implantablemedical device comprises a hermetically sealed housing having at leastone hermetic electrical feed through. An acoustic lead is provided, theacoustic lead having a proximal end connected to the electrical feedthrough, and a distal end configured for transmitting and receivingacoustic signals. The acoustic lead includes an ultrasonic acoustictransducer comprising one or more piezoelectric discs. In variousembodiments, the transducer may be coupled to a distal portion of theacoustic lead, or alternatively, to a proximal portion of the acousticlead. For example, the transducer may be coupled to a proximal portionof the lead, wherein the distal portion of the lead comprises a waveguide.

The device may further comprise means for anchoring the acoustic lead toa location in a body lumen. For example, the means for fixing the leadcomprising one or more items selected from the group comprising a radialanchor, a hook, a screw, and an elastic band. In one embodiment, thedevice further comprises an electrical lead coupled to the housing,wherein the acoustic lead is fixed to the electrical lead.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of embodiments of theinvention, in which similar elements are referred to by common referencenumerals. With the understanding that these drawings depict onlyexemplary embodiments of the invention, and are not therefore to beconsidered limiting its scope, the embodiments will be described andexplained with additional specificity and detail through the use of theaccompanying drawings, in which:

FIGS. 1 a-1 d depict embodiments of an exemplary acoustic transducerconstructed on an internal housing surface of an active medical implantdevice, such as an IPG or a drug pump.

FIGS. 2 a-2 b and 3 a-3 c depict alternate acoustic transducer designscoupled to an internal housing surface of an active medical implantdevice.

FIG. 4 depicts exemplary configurations of an acoustic transducerintegrated on an end of an implantable acoustic lead, whereby theline-of-sight of the transducer(s) may be optimized relative to thelocation of a second implant.

FIG. 5 depicts an alternate configuration of an acoustic lead, in whichacoustic waves are transmitted (or received) at a distal end of a leadtube serving as a wave guide, and in which the acoustic transducer islocated close to (or within) an active medical implant device andcoupled to the lead tube.

FIG. 6 depicts a further alternate configuration in which an acousticlead is fixed to another lead using an elastic band.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The present invention is directed to an (active) implantable medicaldevice such as a pacemaker, implantable cardioverter defibrillator(ICD), Cardiac Rhythm Therapy (CRT), a standalone hemodynamic monitor,or implantable drug pump, which communicates with another implanteddevice (not shown), or an extracorporeal device (not shown), using anacoustic communication link. Towards this end, the active implantabledevice is provided with an acoustic transducer capable of transmittingan acoustic pulse sufficient for activating an acoustic switch in thereceiving device, such as described in U.S. Pat. No. 6,628,989. For thispurpose, an acoustic pulse that is at least 0.1 msec wide, and at leasta 50 Pa peak pressure is preferred. For example, a pulse of 0.5 msec and500 Pa may be used in one embodiment. The acoustic transducer ispreferably capable of transmitting acoustic pulses at a pressure of atleast 0.05 Pa (measured at 20 cm in vitro) and receiving signals of 0.05Pa. The frequency range at which the system can operate is preferablywithin a range of 20 KHz-3 MHz. In order to maximize the efficiency ofthe transducer, it is preferably designed to operate at its resonancefrequency.

In one embodiment, the acoustic transducer is constructed on an internalsurface of the implantable device housing, typically a hermeticallysealed enclosure, with a portion of the enclosure housing wall coupledto the transducer and acting as a vibrating diaphragm. FIG. 1 adiscloses one such acoustic transducer, in which a pair of piezoelectricdiscs 160 are coupled to an internal flat surface of a hermetic implantenclosure wall 110, wherein the portion 135 of the wall 110 to which thetransducer discs 160 are attached acts as a vibrating diaphragm.

Piezoelectric materials are well known and the proposed design of thetransducer can use any material from the group including:electrostrictive ceramic, piezoelectric ceramic, piezoelectricceramic-polymer composite and piezoelectric polymers. The proposeddesign can employ one or more piezoelectric discs with an electrodethere between discs. For example, transducer 160 has two discssurrounding an electrode 155. This structure allows for electricalconnection of the piezoelectric discs in series, in parallel, or in acombination of the two, using electrical contacts to the discelectrodes. Three respective leads 130, 140 and 150 are provided forthis purpose, which allows for optimization of the transducer 160 forperforming specific tasks.

The voltage available in an IPG is usually relatively low, produced fromits internal 2-3 volt battery. For transmitting an acoustic signalrequired for activating an acoustic switch, a relatively high voltagemay be required (for example, several hundred volts). Using multiple,thin discs of piezoelectric material connected in parallel will producethe equivalent acoustic power of a single, thicker disc, but at asubstantially lower voltage. For example, two piezoelectric discs thatare each 0.5 mm thick, connected in parallel, will produce a similaracoustic power as a 1 mm thick piezoelectric disc at half the voltage.However, if one wishes to optimize the receiving sensitivity of thetransducer, serial connection of the thin piezoelectric discs willresult in a higher voltage signal per a given acoustic signal, than asingle thick disk. The ceramics may also be connected anti-parallel, toproduce a bending moment as a piezoelectric bimorph.

For producing the transmitted acoustic signal, the proposed acoustictransducer should be efficient and durable. Preferably, the transducersshould work at their resonance frequency in order to optimize theefficiency and sensitivity of the transducer. The acoustic transducer ofFIG. 1 a belongs to a family known as flexural transducers. Itsresonance frequency depends on several parameters, including the type,thickness and diameter of the piezoelectric material 160, the materialand thickness of the diaphragm 135, and the material, diameter,thickness, and height of a rigid ring 170 attached to the wall surface110 surrounding the transducer and defining the diaphragm 135. Forexample, an acoustic transducer with the following parameters will havea resonance frequency of about 40 KHz: piezoelectric ceramic discs (160)that are 1 mm thick and 10 mm diameter; titanium diaphragm (135) that is1 mm thick and 13 mm in diameter; and a surrounding titanium ring (170)of at least 1 mm in height with an outer diameter of 20 mm. Changing theresonance frequency can be done by modifying the various parameters aswill be appreciated by those skilled in the art of acoustic transducerdesign.

The piezoelectric discs 160 can be coupled to the diaphragm by variousknown methods including using an adhesive, an electrically conductiveadhesive, gel or liquid coupling, or by a direct fabrication of thepiezoelectric material 160 on the diaphragm 135. In FIG. 1 a, thediaphragm 135 is part of a hermetic enclosure wall 110, with itsvibrational modes defined by its thickness and by the material anddimensions of the concentric rigid ring 170 attached to it. The ring 170can be attached to the diaphragm using, for example, welding, brazing,diffusion bonding, adhesive or machining.

An alternate configuration (shown in FIG. 1 b) is achieved by forming agroove 105 in the enclosure wall 110, and attaching the piezoelectricdiscs 160 to a very thin diaphragm portion 135 of the wall, i.e., withinthe grove. This embodiment is more suitable where the enclosure wall 110is relatively thick. Another alternative, (shown in FIG. 1 c) is toproduce an indent 107 in the wall 110 by stamping or coining, or byattachment of a separate diaphragm member 137, including a concentricring portion 125. The parts can be attached by any conventional method,such as, e.g., welding, brazing, diffusion bonding, adhesive ormachining. For optimizing the receiving sensitivity of the transducer, aseparate disc of a piezoelectric material with high acoustic sensitivitycan be used, such as a layer of PVDF, attached to the piezoelectricceramic discs 160 used for transmission. Another way to improve thereceiving signal to noise is by integrating an amplifier 165 to the discstructure 160 (shown in FIG. 1 d), in order to minimize parasiticeffects and noises. It will be appreciated that the addition of theamplifier shown in FIG. 1 d may be equally applicable to the otherembodiments disclosed and described herein.

In an alternate embodiment, a transducer whose properties aresubstantially independent of the enclosure wall is preferred. VariousIPGs and other active medical devices may have different enclosurematerial, thickness and thermal treatment as well as tolerances on eachof these parameters. The resonance frequency and as a result theperformance of a transducer that uses the wall of the enclosure as adiaphragm may vary significantly due to these changes, or the wallproperties may be unsuited to yield the desired transducer properties.

For these reasons it is advantageous to have a transducer in which theacoustic performance is governed by the transducer structure detachedfrom the enclosure wall. An example of such a design is given in FIG. 2a, in which the piezoelectric discs 160 are mounted on a separatemembrane, that is itself mounted to the enclosure wall surface 110. Inthe illustrated embodiment, the membrane 132 may be metallic and has anintegrally formed annular ring portion 120 that surrounds thepiezoelectric discs 160 in a manner similar to ring 170 in theembodiments of FIGS. 1 a and 1 d.

For example, in an IPG, the enclosure wall is usually made of titanium,with a wall thickness of about 0.125 mm-0.5 mm. On the other hand, themetallic membrane 132 and the piezoelectric ceramic discs are preferablyeach about 1 mm thick, i.e. such that the influence of the relativelythin enclosure wall 110 on the performance of transducer issubstantially small. Other thickness and diameters of materials can beused as will be apparent to those skilled in the art of designingacoustic transducers.

FIG. 2 b depicts a variation of the embodiment of FIG. 2 a. The naturalmode of vibration of a transducer surface may include areas whichvibrate in opposite directions, which may harm the acoustic performance.It is possible to optimize the motion transferred to the metallic casingby mounting the transducer on a pedestal 136, such that only surfaceswhich move together are coupled to the enclosure wall 110. For example,in FIG. 2 b, the membrane enclosure 132 (including therein thetransducer discs 160) is coupled to the enclosure wall 110 by a metallicor polymeric material disc 136, whose diameter is less than that of thetransducer disc(s). In such configuration, only the motion of the centerportion of the transducer couples to the wall 110 and to the acousticmedium, while the motion of the edge, which may be of opposite polarity,is not. As will be apparent, other methods of attachment can be designedto fit to specific transducer and enclosure structures.

Another family of transducers that can be useful for embodiments of theinvention is shown in FIGS. 3 a-3 c, and is known as a “flex-tensional”transducer. This device is based upon the principles of theflextensional actuator design. Specifically, an actuator having anelectro-active substrate 520 is used, the actuator having at least oneand preferably a pair of planar or domed surfaces driving end caps. Theuse of flextensional principles provides significant improvements inimplantable output actuators as the available space in the implantabledevice enclosure is limited. The use of the inventive output actuatordescribed herein allows for movement of a piezo to translate into aproportionally larger movement of the flextensional actuator.

The lever action of the end caps in the flextensional devices alsodecreases the effective impedance of the piezo to match optimally theimpedance of the body part being driven. Two configurations arepresented, one (shown in FIG. 3 a) in which the transducer 520 isattached about an outer circumference of the disc 520 to a supportstructure 510, the support structure 510 being attached to the enclosurewall surface 110 and elevating the transducer disc 520 there from, so asto allow the disc 520 to flex into a space 530 defined between the disc520 and the enclosure wall 110. A pair of electrical leads are provided,one (142) coupled to the transducer disc 520, and the other (152) to thesupport structure 510. A second configuration design (shown in FIG. 3 b)is where an additional metallic membrane 535 is provided for attachingthe support structure 510 to the enclosure wall 110, the membrane 520being substantially stiffer than the enclosure wall 110, therebyminimizing the influence of the wall 110 on the performance oftransducer. The embodiment of FIG. 3 c incorporates the features of bothFIGS. 2 b and 3 b, wherein the metallic membrane 535 is itself mountedto a metallic center pedestal 136.

The embodiments described above use several transducer configurations,however other transducer configurations and/or variations and/ormodifications of the concepts herein taught may appear to those skilledin the pertinent art. Integrating the acoustic transducer within themedical device enclosure is practically transparent to the implantingphysician. Also in this configuration the hermetic enclosure protectsthe transducer and its electronics from the environment. However,usually the implantation location of the active medical device islimited due to its size and the wish to minimize the implantationprocedure invasiveness. As a result the implantation site can besub-optimal for acoustic communication. For example, an IPG is mostoften implanted under the skin beneath the collar bone. Due to anatomyand the physical fact that acoustic waves can not cross the lungs, anycommunication between the IPG and a second implant located within theheart may be sub-optimal.

FIG. 4 illustrates another embodiment of the invention, in which thelinkage between the location of the IPG 305 and that of the transduceris disconnected. As shown in FIG. 4, an acoustic transducer, alternately320 or 330, may be located at the tip of a lead 300, referred to hereinas an “acoustic lead.” The acoustic lead 300 can be similar to anelectrical lead commonly used in IPGs (e.g., for pacing). In a preferredembodiment, the acoustic lead 300 is not positioned within the heart,but rather in a vein leading to the right atrium, e.g. the subclavianvein, the cephalic vein, the right or left brachiocephalic vein, thesuperior or inferior vena cava or the internal jugular vein. Theconnection of the said acoustic lead 300 to the IPG 305 can be via astandard electrical hermetic feed through 303 of the IPG 305.

Implantation of the acoustic lead 300 can be performed using the samecatheterization techniques used for implanting IPG electrical leads.However, instead of entering the right atrium (and in some cases theheart right ventricle), the acoustic lead can preferably be locatedexternal to the heart, and preferably in a location with a direct “lineof sight” between the lead acoustic source and the second implant. Manyof the risks involved in implanting an IPG electrical lead, such asthrombus formation or damage to the heat valve, may be avoided by notentering the heart or passing through the heart valve. The fixation ofthe acoustic lead 300 may be accomplished, for example, by a radialanchoring of the device to a wall of the vessel using a stent-likedevice, or with a screw or hook-type fixation to the vessel wall.

Alternatively, an acoustic lead can be fixed to another lead using, forexample, an elastic band 640, as shown in FIG. 6. In this configuration,a first electrical lead 630 extending from an IPG 660 is implanted (forexample) for pacing in the patient's right ventricle 610. A guide wire,and preferably a catheter, are threaded into an elastic band 640attached on or around the first electrical lead 630. An acoustic lead650 may then be implanted over the wire or the catheter. This proposedprocedure should be considered only as an example, and other techniquesand methods of implanting and fixating an acoustic lead will be apparentto those skilled in the art.

An acoustic transducer 655 is integrated at the tip of the acoustic lead630, and can be of any type of transducer. For example, FIG. 4 shows theexemplary use of two designs discussed previously, a flexuralconfiguration 310, and a flex-tensional design 330. Preferably thetransducer electrical contacts and leads to the IPG are isolated frombody fluids. Since the impedance of the transducer will be similar inmagnitude to the impedance of the IPG leads (on the order of severalhundreds of ohms), the same isolation techniques used for standard IPGleads can also be used for the acoustic lead. Also, the diaphragm of thetransducer 350 can be coated with the same polymeric material of thelead, e.g. polyurethane or silicone. However, care should be taken thatgas bubbles will not be preserved in this layer, so as not to attenuatethe acoustic wave transmission.

Another embodiment, including another acoustic lead configuration, isshown in FIG. 5. In this embodiment, the acoustic lead is based on anacoustic wave-guide 450 coupled on one end to an acoustic transducer400. In this configuration, the acoustic waves propagate along, and exiton a far end 405 of, the wave guide 450. The acoustic transducer can beexternal to the IPG (as shown in FIG. 5), or integrated within the IPGenclosure (not shown). Preferably a funnel shaped structure or a gradualchange of the material properties through which the sound wavespropagate (420 to 430) is used to optimize the coupling of thetransducer to the wave-guide by matching their mechanical impedances.This configuration allows the usage of a larger transducer for producingthe acoustic waves, while still directing the acoustic energy to anoptimized location, using a small size, catheterization compatiblewave-guide. Again, the transducer can be of any desired type andconfiguration.

The design of the wave-guide 450 should ensure that a substantial partof the acoustic energy produced by the acoustic transducer module 400will be emitted at the lead far end 405. The material of which thewave-guide is preferably made of, or filled with, a good acousticconductor. Liquids, including water and saline, or polymers, such aspolyurethane, nylon, or rubber, can be used for this purpose. The wall430 of the lead 450 should serve as a reflector for the acoustic wavesto prevent leakage of the acoustic energy out of the wave-guide. Thewall 430 can be made of a substantially rigid material such as a metaltube, or a polymer tube radially reinforced with metal or glass fibers.

Alternatively, the waveguide 450 may consist of a flexible metal tube orwire, which conducts the acoustic vibrations via longitudinal waves.Such metal wire or tube may be encased in a thin solid or gas-containingcladding, which insulates it mechanically from the surrounding fluid.The far end of the wave-guide 405 serves as an acoustic wave sourceacoustically coupled to the body. For example, a thin membrane 440,e.g., made of a polymer or a metal, may serve as the acoustic diaphragm.This acoustic membrane 440 may be resonant at the desired frequency ofoperation, in order to increase its effectiveness as an acousticradiator. Alternately, the far end of the lead may contain a resonantstructure, such as a mechanical structure or a Helmholtz resonator,coupled to the membrane 440.

All the above-disclosed, implantable transducers can, in addition toactivation and communication with a second implant, also be used foracoustically energizing and charging the second implant. Preferably, theacoustic lead designs of FIGS. 4 and 5 should be used for this purpose,taking advantage of the optimized location of the transducer in theseconfigurations relative to the second implant. The possible line ofsight between the lead transducer and the second implant, combined withthe possible small distance between them, which can be between a fewmillimeters to several centimeters, can significantly reduce therequired energy for charging the second implant battery or capacitor.The charging can be done using energy from the IPG battery, or from anextracorporeal power source (either telemetrically, or by making a smallincision at the IPG implantation site), disengaging the acoustic leadfrom the IPG controller, connecting the acoustic lead to an externalpower source, and using the acoustic energy produced by the acousticlead to charge the battery within the second implant.

Preferably, the battery capacity of the second implant is such thatcharging will be not be required for a duration longer than that of theIPG battery. Upon the replacement of the IPG controller, the acousticlead can be connected to an external power source for charging thesecond implant battery. Alternatively, an acoustic catheter can be usedfor acoustically charging the second implant. This catheter can be builtsimilar to the acoustic lead, with an acoustic transducer at its tip orby serving as an acoustic wave-guide. The acoustic catheter can beintroduced to the body in a similar technique used for right heartcatheterization. This procedure is usually carried out via the femoralvein and internal jugular subclavian vein, using a standard guide wirebased catheterization or by a floating balloon (e.g., a Swan-Ganzcatheter). The procedure can be guided using fluoroscopy or pressurepattern measurements. Since the acoustic source on the catheter can belocated very close to the second implant, the charging process ispreferably very efficient and local.

1. An implantable medical device adapted to be acoustically coupled to asecond medical device, the implantable medical device comprising: ahermetically sealed housing having a housing wall with an interiorsurface; an ultrasonic transducer disposed within the housing andconfigured to acoustically couple to the second medical device, theultrasonic transducer configured to transmit an outgoing acoustic signalto the second medical device and receive an incoming acoustic signalfrom the second medical device; a metallic membrane interposed betweenthe interior surface of the housing wall and the ultrasonic transducer,the membrane configured to couple the ultrasonic transducer to theinterior surface of the housing wall; and wherein the ultrasonictransducer is configured to operate at a resonance frequency at or above20 KHz.
 2. The device of claim 1, wherein the ultrasonic transducerincludes one or more piezoelectric discs.
 3. The device of claim 2,further including an annular ring radially surrounding the one or morepiezoelectric discs and attached to the interior surface of the housingwall.
 4. The device of claim 2, wherein the one or more piezoelectricdiscs comprise two discs, and further including an electrode positionedbetween the piezoelectric discs.
 5. The device of claim 4, furtherincluding a respective electrical lead coupled to each of the twopiezoelectric discs and the electrode.
 6. The device of claim 2, furtherincluding an amplifier integrated with the one or more piezoelectricdiscs, the amplifier configured to minimize parasitic effects and noisein the incoming acoustic signal received from the second medical device.7. The device of claim 2, wherein the membrane has a substantiallygreater thickness than a thickness of the housing wall.
 8. The device ofclaim 7, wherein the membrane is mounted on a pedestal, the pedestalattached to the interior surface of the housing wall, the pedestalhaving a smaller diameter than each of the one or more piezoelectricdiscs.
 9. The device of claim 1, wherein the second medical device is animplantable device.
 10. The device of claim 1, wherein the secondmedical device is an extracorporeal device.
 11. The device of claim 1,wherein the implantable medical device is an implantable pulsegenerator.
 12. An implantable medical device adapted to be acousticallycoupled to a second medical device, the implantable medical devicecomprising: a hermetically sealed housing having a housing wall with aninterior surface; an ultrasonic transducer disposed within the housingand configured to acoustically couple to the second medical device, theultrasonic transducer including one or more piezoelectric discsconfigured to transmit an outgoing acoustic signal to the second medicaldevice and receive an incoming acoustic signal from the second medicaldevice; an annular ring radially surrounding the one or morepiezoelectric discs; and wherein the ultrasonic transducer is configuredto operate at a resonance frequency at or above 20 KHz.
 13. The deviceof claim 12, wherein the one or more piezoelectric discs comprise twopiezoelectric discs, and further including an electrode positionedbetween the piezoelectric discs.
 14. The device of claim 13, furtherincluding a respective electrical lead coupled to each of the twopiezoelectric discs and the electrode.
 15. The device of claim 12,further including an amplifier integrated with the one or morepiezoelectric discs, the amplifier configured to minimize parasiticeffects and noise in the incoming acoustic signal received from thesecond medical device.
 16. The device of claim 12, wherein the annularring is attached to the interior surface of the housing wall.
 17. Thedevice of claim 12, further including a metallic membrane integratedwith the annular ring, the membrane interposed between the interiorsurface of the housing wall and the ultrasonic transducer.
 18. Thedevice of claim 17, wherein the membrane has a substantially greaterthickness than a thickness of the housing wall.
 19. The device of claim17, wherein the membrane is mounted on a pedestal, the pedestal attachedto the interior surface of the housing wall, the pedestal having asmaller diameter than each of the one or more piezoelectric discs. 20.The device of claim 12, wherein the second medical device is animplantable device.
 21. The device of claim 12, wherein the secondmedical device is an extracorporeal device.
 22. The device of claim 12,wherein the implantable medical device is an implantable pulsegenerator.
 23. An implantable medical device adapted to be acousticallycoupled to a remote device implanted within the body, the implantablemedical device comprising: a hermetically sealed housing having ahousing wall with an interior surface; an ultrasonic transducer disposedwithin the housing and configured to acoustically couple to the remotedevice, the ultrasonic transducer configured to transmit an outgoingacoustic signal to the remote device at a frequency at or above 20 KHz;and a metallic membrane interposed between the interior surface of thehousing wall and the ultrasonic transducer, the membrane configured tocouple the ultrasonic transducer to the interior surface of the housingwall.